The body's primary daily needs are: oxygen, food & drink, removal of wastes. Sustenance diets satisfy these needs by definition. I hypothesize that food utilization will be best when only the amount sufficient for sustenance is eaten. Eating greatly in excess of sustenance overwhelms the transport and storage systems of the body. Food components and metabolites are dumped into the tissues. This impedes the free circulation of the nourishing and cleansing blood. The cells suffer from lack of oxygen, nourishment and inadequate waste removal. Disease shortens Life.

The diets of all mammals in the wild are also sustenance diets. E.g. the herds of grazing animals in the steppes grew in numbers until the available grass set a limit to it and evolution had adapted the animals to this limited number.